Insulin resistance can be assessed by the euglycaemic clamp technique. To date, this is the golden standard, but it is not suited for clinical practice. A 13C glucose breath test will be tested as a valid alternative. The curve of the exhaled 13C CO2 as a function of glucose metabolism can be correlated to the curve of the glucose disposal rate obtained via the clamp technique.

The hyperinsulinemic-euglycemic clamp technique is the golden standard to assess insulin resistance in type 1 diabetes subjects. The plasma insulin concentration is acutely raised and maintained at 100 μU/ml by a continuous infusion of insulin. Meanwhile, the plasma glucose concentration is held constant at basal levels by a variable glucose infusion. When the steady-state is achieved, the glucose infusion rate equals glucose uptake by all the tissues in the body and is therefore a measure of tissue insulin sensitivity.

These data will be compared with the results of a 13C glucose breath test. Breath tests using 13C substrates are based on the principle that 13C CO2 in the exhaled breath can be measured as a metabolic tracer.

Breath testing has a major advantage over the clamp test in that it can be performed non-invasively and repeatedly without necessary supervision by medical staff.

Inclusion Criteria:

• Adult type 1 diabetes patients
• 25/50 subjects with confirmed NAFLD (using ultrasound criteria)

Exclusion Criteria:

• pregnancy
• gastric bypass surgery
• cirrhosis
• secondary cause of liver steatosis present
• any cause which makes a 4-hour clamp impossible

Type 1 diabetes subjects from the research facility's outpatient clinic.